SE450496B - COMPOSITION TO PREPARE A NON-LEADING GLASS MOVIE ON SURFACES OF ORIENTED SILICON-ALLOY STEEL AND WAY TO PREPARE THE COMPOSITION - Google Patents

Description

10 15 20 25 35 450 496 between magnesia and the fayalite surface layer. An active magnesia of the type commonly used hydrates with the accompanying increase viscosity of the magnesia water slurry and its take creates a problem because the viscosity of the slurry must be kept within an area which allows the application of a coating with even thickness by dipping, spraying, dosing rollers, or similar. E ' Inactive magnesia has never before been considered suitable for form a non-conductive glass film on oriented silicon alloy steel strip and sheet metal because the dense particles could not be in suspension resulting in the formation of a slurry with very low viscosity. The dense inactive particles should also do not react with the fayalite surface layer, at least within the time limits prescribed by commercial production tigheter.

However, since inactive magnesia is available to much lower cost than active magnesia, offers exchange mott inactive magnesia in an annealing insert composition the prospect of a very significant economy in the treatment of on-edge-oriented silicon alloy steel. IN Although additives to magnesia slurries have been suggested for the purpose of improving the glass film properties and / or for to facilitate the magnesia-fayalite reaction has, as far as we know, down for nesia and increase its viscosity. to no additives developed, which are successful stabilization of a slurry in water of inactive The addition of phosphates to a slurry of active magnesia is known; to improve the glass film properties and the mag- the net properties of the silicon alloy steel material.

Reference is made here to U.S. Patent 3,615,918 (J.D. Evans and Dgw. Taylor), in which a magnesia composition containing a decomposable phosphate compound is described. According to this patent reduces the phosphate, which is included between 1% and 25% by weight calculated SOW P205 to elemental phosphorus below it 10 15 20 25 30 ß 450 496 final annealing at high temperature, which diffuses inwards when coating into the silicon alloy steel.

Phosphate-based coatings, which can be applied directly to metal surfaces, or as secondary coatings over a work-glass coating magnesia base, are known in the art. Phosphate and magnesia containing coatings are suitable for application to orientation the silicon alloy steel surfaces, either directly or as secondary coatings disclosed in U.S. Patents 3,840,378 and 3,948,876 (J.D. Evans).

As stated above, as far as we know the previously known technology has never suggested the use of inactive magnesia for a composition intended to be used as an annealing intermediate oriented, silicon alloy steel strip and sheet metal, no, nor have additives have been proposed which would remedy the of an inactive magnesia for this purpose.

It is a principal object of the present invention to provide a magnesia slurry in water with a high concentration containing an essential part of inactive magnesia, which exhibits a citric acid activity greater than 200 seconds, which is stable 7 against sedimentation, which has a viscosity suitable for brought by ordinary means and which will react with the fayalite layer on the material surfaces and form a uniform non-conductive glass film of satisfactory quality. in The invention further aims to provide a method for suspend an inactive magnesia in water to produce a car slurry, which can be easily applied to silicon alloy steel surfaces and which will react to form a non-conductive glass film during a subsequent annealing at high temperature.

According to the invention, there is provided a composition for forming an ic- conductive glass film on surfaces of oriented silicon alloy steel and sheet metal thereof, comprising a slurry in water of gastric nesia and a phosphate-containing compound selected from the group consisting of 10 15. 20 25 30 35 V _..__.....-, ....._. , time greater than 200 seconds, 450 496 calcium phosphates, water-soluble ammonium polyphosphate, aluminum nium phosphate, magnesium phosphates, phosphoric acid and mixtures thereof, where the compound is present in the range of 2% by weight 25% by weight, calculated as P2O5, based on the magnesia weight and essentially residual water, which composition is characterized by that at least 25% by weight of magnesian has a citric acid activity greater than 200 seconds, that the magnesium concentration is up to 0.6 g per cm 3 of slurry, and that the slurry is car against sedimentation for time periods of up to 10 hours mar.

The present invention further relates to a method of suspending an inactive magnesia in water to produce a slurry, which is stable against sedimentation and which after being applied surfaces of oriented silicon alloy steel strip or sheet metal, more to react and form a non-conductive glass film during subsequent annealing at high temperature, where the method that at least 25% by weight of the magnesia has a lemon content acid activity greater than 200 seconds, a phosphate-containing compound selected from the group consisting of calcium phosphates, water-soluble monium polyphosphate, aluminum phosphate, magnesium phosphates, phosphorus acid and mixtures thereof, where the compound is present within range 2 to 25% by weight calculated as PZOS, based on weight of the nesian and thereafter consists essentially of water, at the magnesium concentration is up to 0.6 g per cm3 of slurry where the slurry is stable to sedimentation over time. periods of up to 10 hours.

It has been found that the invention can be practiced successfully inactive magnesia from commercial source with a citric acid active a Cl- level of 0.02% maxi- mum and an SO4 level of 0.02% maximum. Tests have been completed on such magnesia having a citric acid activity extending from about 1500 to about 3000 seconds, where it active magnesia comprised 100% of the total magnesia content in the slurry. Mixtures of 50% by weight of inert magnetic sia with S0 weight percent active magnesia has also been tried and has have been found to provide optimal adhesion to the dried coatingsx on: nate- 10 15 20 ' 25 30 35 c magnesia can also be used, down to 10% inactive magnesia 450 496 material and improved the quality of the glass film. It is obvious that lower proportions of inactive magnesia along with an active and 90% active magnesia for improved glass film quality, though the economic advantage of inactive magnesia is thereby reduced lorad. On the other extreme direction has satisfactory results obtained with slurries where 100% of the magnesian had P8 ' a citric acid activity greater than 200 seconds. The main the umbilical part when using a composition in which all nesian is inactive is derived from the fact that the dried the adhesion of the installation is only good so that care must be taken is practiced when handling the coated rings to prevent the magnesium coating to be removed. Where the inactive magnesia constitutes 25% to 75% of the total magnesia content, the ta problem. This area is thus preferred. The active mag- nesian preferably has a citric acid activity of about 20 to RO seconds.

The phosphate additive not only stabilizes the inactive magnesium the slurry against sedimentation, 'but also increases the viscosity to an area desirable to apply the same with common agents such as dipping, spraying, dosing rollers and similar. In addition, the magnesium concentration may be higher than in corresponding prior art slurries, which contain a dast active magnesia. Such high concentrations are advantageous. by drying can be achieved with less heat and in a shorter time and that loss of annealing can be maintained during > 1%. With such low annealing losses, it has been found that the glass film quality remains very even both along the length and the width of a ring.

Preferred phosphate compounds are monocalcium phosphate compounds. monohydrate, dicalcium phosphate dihydrate and water-soluble ammonium 'um-polyphosphate. Preferably from 2.5% to 10% by weight is added calculated as P205, based on magnesia weight. When adding monocalcium phosphate monohydrate or dicalcium phosphate dihydrate, which is in granular form, the material can be dry blended with magnesian 10 15 20 25 35 450 496 before the formation of a water slurry, or may be added the water before, during or after mixing the magnesia with it.

The manner and step in which the phosphate compound is incorporated carried in the slurry thus does not constitute a restriction ' in the practice of the invention. When it comes to water soluble ammonium polyphosphate, which is available only as an aqueous solution, the addition is made to the water in the water slurry either before or after admixture of magnesia.

The high firing temperatures used in the production of inactive magnesia results in sintering and / or agglomeration of magnesia, which produces a dense particle, which requires _ grinding to obtain the desired particle size distribution.

This grinding produces magnesium particles with an active surface.

Although we do not wish to be bound by theory, it is assumed that the barrel compound added in accordance with the present invention reacts with the magnesia particles to form a thin film phosphate layer on the surface of the particles. This thin phosphate layer (P2O5_) gives the particles a net-negative charge, which prevents aggregation lomeration and sedimentation to occur. This is supposed to be the theoretical basis for the markedly improved stability against sedimentation, which has been observed. In addition, increases the stable suspension of such magnesia particles of the slurry viscosity to a desired range. IN 3 turned without sedimentation and without increasing the viscosity It has been found that concentrations up to 0.6 g / cm an undesirable extent when the magnesium component is present of 100% inactive magnesia. When using a mixture of 50% inactive and 50% active magnesia, concentrations can be used 3 to about 0.36 g / cmš.

Dried coating weights of about 7.5 to about 25 g / m2 ranging from about 0.2H g / cm was obtained with the above concentration ranges, then the slurry was applied in the usual way with dosing rollers.

The amount of phosphate-containing compound that can be added depends on the conditions of decarburization and final annealing with a 1., l0 15 20 25 35 450 496 relatively low phosphate level for highly oxidizing decarburizing conditions and a relatively high phosphate level content for less conditions.

Comparison between a 100% inactive magnesia slurry containing a phosphate compound in accordance with the present invention with a control slurry containing 100% of the same inactive magnesia slurry but without addition indicated that it existed no appreciable sedimentation of the collection. the finding after 10 hours, while the slurry without additive sedimented completely within an hour and left a substantially clear on top of liquid layer.

As a background, it should be pointed out that flzkall rolled carbonated silicon alloy steel strip and sheet metal can be prepared by standard processes, in which a suitable melt is cast in the form of ingot or continuously cast into platinum. If the melt is dropped ingot, the steel is pre-rolled in the usual way and the platinum to an intermediate thickness from a temperature of about g1200 ° C to about 130,000 with annealing after hot rolling.

The glow plugs from the hot rolling are removed and the material then rolled to final dimension in one or more steps, followed by decarburization, preferably in a humidified hydrogen atmosphere. sphere. If the steel is continuously cast to platinum form follows preferably the procedure shown in U.S. Pat. tent 3 76fl # 06 (M.F. Littman). A magnesia coating is then applied to the surfaces of the decarburizer. the material by dipping, spraying, dosing rollers or other common means. The coating is then dried by heating to a temperature sufficient to evaporate the water.

The dried coating weight should preferably be within the range between about 6 and 20 g / m2. The coated material 'is then subjected to a final annealing at high temperature at about 10950 to about 126000, which may be a coffin annealing or an annealing with open rings in a reducing action. _mosphere. During this annealing, the magnesia reacts and forms 10 15 20 25 35 450 496 a non-conductive glass film and the cube-on-edge orientation are obtained by secondary recrystallization.

The composition and method of treating the silicon alloy steel to final strip and plate form does not constitute a limitation in present invention. Any of the regular quali- the qualities or or the qualities with high permeability of oriented silicon alloy steel on which a magnesium coating used can be treated in the practice of the present invention. ning. As non-limiting examples may be mentioned that compositions and methods in which the present invention finds use include takes those disclosed in U.S. Patents 3,287,183; 3,873,381; 3 905 8525 3 905 345; 3,932,255; 5,957 5ü6 and U 000 015.

With the exception of No. 3,932,23ü, these patents relate to production of materials with high permeability (relative permeability meaability greater than 1850 at 796 A / m) by additions of boron and nitrogen to the steel. Manganese and sulfur (and / or selenium) may also be present. n I For a regular grain-oriented silicon alloy steel, where manganese and sulfur (and / or selenium) are present as barley growth inhibitors, a representative but non-limiting composition may be on the cold-rolled.and charred material comprises in weight% about 2% to conversion Ä% silicon, about 0.01% to about 0.1% manganese, about 0.01% to about 0.03% sulfur, about 0.002% to about 0.005% carbon, up to about 0.065% (total) aluminum and the rest iron plus temporary contaminants.

Two series of laboratory tests were performed, which showed phosphate the efficiency of the batch to an aqueous slurry of an active magnesia. In both test series, the magnesia came from commercial source and had a citric acid activity of about 2000 seconds.

The phosphate compound used was monocalcium phosphate. monohydrate (marketed by Stauffer Chemical Company under the name "12 XX" and marketed by Monsanto Corporation under the the drawing "MC.P."). Both were in grain form. 10 15 20 25 30 35 450 49š In the first series, slurries in water were prepared each containing 0.6 g of magnesia per omz, wherein it the first slurry did not contain any additive and the The standing slurries contained 2.5%, 5%, 7.5% and 10% residual respectively of the calcium phosphate calculated as PQO5, based on magnesiavikten. Decarburized silicon alloy steel material with a thick play of 0.56 mm was coated with each of the slurries. Up- the slurry which did not contain any additive and the slurry containing 2.5% phosphate did not wet the material well and without stirring, the magnesian tended to settle out rapidly.

No problems were observed when coating with the other slurries. the ings.

After a final annealing at high temperature at 1200 ° C indicated a study of the glassware developed on each sample the film, that they stretched from a thin rainbow glass for the composition which did not contain any additive to a light gray continuous film for the slurries containing more than 5% phosphate. A progressive improvement of the physical nature of the glass film appearance was noted for each higher amount of phosphate additive.

The second series involved the preparation of slurries containing 100% inactive magnesia by 0%, nominally 5%, 7.5% and 10% additions of calcium phosphate calculated as P 50% by weight a citric acid activity of about 30 seconds by 0%, nominal 2.5% and 5% calcium phosphate calculated as P2O5 and 50% by weight % inactive magnesia with 50% active magnesia from another source 0 n 2 5 ' inactive magnesia with 50% by weight of active magnesia with with a citric acid activity of 30 seconds by 0%, nominal 2.5% and 5% calcium phosphate, calculated as P2 O5. A con- control composition was also prepared containing 50% by weight. % each of the active magnesia from the two sources with 2.5% by weight addition of calcium phosphate calculated as P205.

The active magnesia preparations used had the following specifications: we 10 15 20 25 35 450 496 10 F-: less than 500 ppm Cl_: less than 200 ppm Na_: less than 200 ppm solution at 100 ° C = 1.5 - 13.0 2 Citric acid activity: 20 to Ä0 seconds.

Particle size: 99.9% through 0.07U mm (200 mesh) In 99.5% by 0.0HÄ mm (325 mesh).

These specifications should be observed in the practice of although the citric acid activity may extend up to less than 200 seconds, as previously indicated.

The slurries in which all magnesia was inactive at a concentration of 0,60 g / cmš, while slurries containing 50% inactive and 50% active magnesia were prepared at concentrations of 0.36 g / cm Control- the slurry was prepared with a concentration of 0.14ü g / cm3.

Decarburized silicon alloy steel barrels with a thickness of 0.28 mm was each coated with the above slurries and was subjected to coffin annealing in a reducing atmosphere at about 120,000. No occupancy problems occurred with anyone of the slurries with the exception of the one that contained only inactive magnesia without any addition of calcium phosphate. All the remaining slurries remained in suspension and wetted the material well.

Evaluation of the glass films formed by the various slurries suggested the following: The inactive magnesia without any calcium phosphate additive forms they a thin, discontinuous glass film.

The slurries of 100% inactive magnesia with additives of 5% and 7.5% calcium phosphate calculated as P2O5, formed a thin, rough, light gray glass film. The slurry containing 100% hrs 10 15 20 25 35 450 496 11 inactive magnesia and 10% by weight of calcium phosphate resulted in a rough, reddish gray glass film of poor quality.

Mixtures of 50% inactive magnesia and 50% active magnesia formed glass films with improved physical appearance. Slam- which did not contain any calcium phosphate additives showed said a continuous gray glass film with a slightly rough texture.

The calcium phosphate additives of 2.5% and 5% counted as P2O5 led to the formation of a smoother, lighter gray glass film.

All the slurries containing 100% inactive magnesia had poor oxidation resistance independent of calcium phosphate the additives.

The slurries containing 50% inactive magnesia and 50% active magnesia without any calcium phosphate additive exhibited also poor resistance to oxidation. Slurry in- containing 2.5% potassium phosphate calculated as P205 showed slightly improved resistance to oxidation. The best oxide was shown by slurries containing 50% inactive and 50% active magnesia with 5% calcium phosphate, calculated _som P205. For comparison, the control sample contained equal parts of the two active magnesia preparations by 2,5% " calcium phosphate additive poor resistance to oxidation.

Secondary coatings of the kind shown in the above U.S. Patents 3,800,378 and 5,908,876 (containing magnesia, phosphate and aluminum) were applied to all samples and tested for adhesion. The adhesion of those secondary coatings followed the same tmy fi as resistance against oxidation. Glass films that showed good oxidation resilience had good adhesion to the secondary coating. while those who had poor oxidation resistance may have shown poor adhesion to the secondary coatings. na. The best adhesion was shown by mixtures of 50% active and 50% inactive magnesia preparations with 5% calcium phosphate calculated as PQO5. 10 15 20 25 30 35 450 496 12 Different magnetic properties of the samples in the second series are was tuned at 60 Hz and is summarized in Table I. It is to be noted that of the compositions containing 100% inactive magnesia it best magnetic quality was exhibited by the sample containing a nominal 5% calcium phosphate additive calculated as P2O5. To- batches of nominal 7.5% and 10% calcium phosphate resulting in a decrease in magnetic quality.

The magnetic quality of samples containing 50% inactive and 50% active magnesia preparation showed a surprising improvement, especially with calcium phosphate additives. Without calcium phosphate additive value magnetic quality comparable to it at the control sample. With calcium phosphate additives at nominal 2.5 and 5%, calculated as P2O5, all samples showed a significant significant improvement in magnetic quality compared to tried.

Work experiments were next performed using decarburized silicon alloy steel in rings with a thickness of 0.28 mm inside the conventional steel composition ranges indicated above and the rings were coated with the following composition: 50% by weight of inactive magnesia CAA 2000 seconds " 50% active magnesia CAA 30 seconds 5% monocalcium phosphate monohydrate, calculated as P205. residual water.

Slurry concentrations and coating weights for the dry The coated coatings are listed in Table II. No coating problems 'appeared. The slurry wetted the tape very well and generated the smooth, even coatings; adhesion in the dried state was good. No significant sedimentation was observed in the coating the trough.

It was found that the coatings dried much faster than usual coatings containing only active magnesia. Consequently 10 15 20 25 35 450 493 _13 you can dry coatings containing inactive magnesia at lower temperature, thereby reducing the amount of energy required gi.

The coated rings were coffin annealed in a reducing atmosphere at about 1150 ° C in the usual way for ZH hours. The rings 'formed an excellent glass film, which was slightly gray, smooth, continuous and free from any oxide or rainbow. In addition from the beginning of the ring to its end there was no variation in the physical appearance of the glass film, which normally occurs at common active magnesia preparations and this not in any of these rings.

Magnetic properties of the above rings are given in Table III together with magnetic properties of control rings from the same charge coated with a mixture of 50% active magnesia CAA 30 seconds from a first source and 50% active magnesia CAA 30 seconds from a second source. It is clear that it the magnetic quality of rings coated with the composition the invention was good and equal to or better than the corresponding those of the control rings.

'Additional tests have been carried out which show that the composition and the method of the present invention is applicable to the product silicon alloy steel with very high permeability, including holding boron and nitrogen in accordance with what is taught in it U.S. Patent 3,873,381 and includes boron and titanium dioxide is added to the magnesia composition. Previously known magnesia compositions to which boron and titanium dioxide additives have been made has always contained only one active magnesia with a lemon acid activity extending from e.g. about 20 to about 80 seconds. The drilling additive may take the form of a drilling rig. such as boric acid, sodium tetraborate and the like.

In these samples a mixture was used as the base composition consisting of 50% by weight of inactive magnesia from a home source with one CAA value of about 2000 seconds and 50% by weight of an active e 450 496 leeward magnesia from a home source at a CAA value of about 30 seconds. An active magnesia from a Japanese source with one CAA value of about 30 seconds was used as a control as this had produced optimal glass film properties and magnetic quality in the production of a material with very high permeability by previous procedures technique. This contained 0.08% boron at delivery.

The base composition was mixed with water to a slurry a concentration of 0.36 g / cm 3 'Different combinations of additives were mixed with slurry samples, based on the total dry magnesia weight as follows: 2 monocalcium phosphate monohydrate as P 2_ ° 5 z Bor z 0102 5 or 0 10 0 0 15 0 0 20 0 0 5 0.12 0 10 "'0.12 0 15 '0.12 0 20 and 0.12 0 5 0 5 10 0 5 15 0 5 20 0 5 5 0 10 10 0 10 15 0 10 20 0 10 450 4960 15 5 1 0.12 5 10 0.12 5 15 0.12 5 20 0¿12 5 5 5 0.12 10 10 0.12 10 15 5 0.12 10 20 0.12 10 10 The control composition was mixed with water to a slurry with a concentration of 0.1U7 g / cmš and 5% titanium dioxide (based on magnesia weight) was added. Coatings were applied to charred substances of silicon alloy steel with very high permeability with a thickness of 0.28 mm and coating weights in the dried state were within a range from 10 to 12 g / m2. The coated substances were then subjected a final annealing in a reducing atmosphere which included At 119,000 in pure hydrogen for 24 hours.

Evaluation of the various coated and annealed substances showed the following results: 7 Samples with 5%, 10%, 15% and 20% calcium phosphate with and without boron additives plus titanium dioxide developed smooth, light gray glass films.

Titanium dioxide additives made the glass film rougher and darker 30 gray. At 5% calcium phosphate and 5% and 10% titanium dioxide were the physical appearance similar to that of the control sample ( containing 5% titanium dioxide). At levels 10%, 15% and 20% calcium phosphate, the glass film was progressively rougher and darker re to the color. 35 Secondary coatings of the kind shown above U.S. Patent 3,8U0,378 was filed. Sample containing 10 15 20 25 35 450 496 16 5% and 10% calcium phosphate plus 5% and 10% titanium dioxide had it best look.

In samples containing no titanium dioxide, the adhesion was to it secondary occupancy poor. The titanium dioxide-containing samples had improved adhesion. The sample containing 5% calcium phosphate and 5% titanium dioxide had adhesion similar to that of the control sample, while the adhesion of the sample containing 10% calcium phosphate and 5% titanium dioxide was superior kbntrollprovets.

With regard to magnetic quality, had samples containing 5%, 10% and 15% calcium phosphate (without boron and titanium dioxide batches) similar properties, ie core losses at 1.7 T and 60 Hz of 1.675 watts / kg and relative permeability of 1875 at 796 A / m.

In the samples containing 0.12% boron and no titanium dioxide, var the magnetic quality inferior to the above sample as did not contain boron and titanium dioxide.

Samples containing titanium dioxide and without boron showed inferior late magnetic quality, _ Samples containing boron and titanium dioxide showed improved genetic quality, the best being obtained with 5% calcium phosphate barrels, 0.12% boron and 5% titanium dioxide. The core loss for the best the sample was 1.679 watts / kg at 1.7T and 60 Hz and relative the permeability was 1880 at 796 A / m compared to 0.763 and 1905 for the control test.

It was further observed that boron additions increased the final grain the size considerably and that calcium phosphate additives larger than 5% (with boron and titanium dioxide) were perishable for the net quality.

It is therefore obvious that in the production of materials 10 15 20 25 30 35 450 496 17 with very high permeability a best combination of properties obtained with 5% to 10% phosphate compound calculated as P2 O5, about 0.10 to about 0.15% live and about 5% to around 10% titanium dioxide, based on the magnesia weight. These areas it is applicable to a magnesia composition, around 25% to about 75% is an inactive magnesia with a citric acid numbers of about 1500 to about 3000 seconds and the remainder is an active magnesia with a citric acid number of about 20 more H0 seconds.

The above data show that calcium phosphate additives are significant changes the reactions that occur and the composition of the glass film during the final annealing at high temperature. The phosphate oxidizes the silicon and iron on the material surface and increases the amount fayalite in the surface, Phosphorus is thus reduced and most of it diffuses without adverse effect into the steel, as is disclosed in the aforementioned U.S. Patent 3,615,918 on the other hand, calcium, in the form of calcium oxide, acts as one flux and causes liquid formation at a lower temperature ratur. The calcium oxide reacts with the fayalite on the surfaces of the silicon alloy steel and forms wollastonite, which is one magnesium and potassium oxide-silica complexes. Wollastonite melts about 20,000 lower than fayalite and this increased amount of liquid phase formation is thus able to take the magnesia in solution easier to complete the glass film formation.

Citric acid activity is a measure of the rate of hydration on the magnesium oxide and is determined by measuring the time that required for a given weight of magnesia to give hydroxyl ions sufficient to neutralize a given weight of citric acid.

The test is the same as mentioned in the US patent 3 8U1 925, viz 1. 100 ml of 0.0000 citric acid in water containing 2 ml of 1% phenolifain indicator is brought to 30 ° C in a can with a capacity of 226.8 g (8 ounces) with at opening. The jar is equipped with a screw cap and a magnetic stir bar. 4soi496ae i -1a 2. Magnesia weighing 2.00 g is introduced into the jar and one stopwatch is started at the same time. 3. As soon as the magnesia sample is added, screw the lid on 5 cans. After 5 seconds, the jar and its contents are shaken cool. Shaking ends after 10 seconds.

U. After 10 seconds, the sample is placed on a magnetic technical agitation assembly. Mechanical agitation should induce one Vortex about 2 about deep in the middle when the inner diameter of the jar is 6 cm. 5. The stopwatch is stopped the moment the suspension becomes cut and the time is noted. This time in seconds is citric acid 15 activity. 10 15 20 25 50 450 496 19 Table I Magnetic properties Approx. (HZPOU) 'H20 Core loss Relative per- mmigiål Weight * S ° m Éåtåškg “d Üïåbååštïïm 5: Mag ës asia "2 5" 1.5 T 1.7 T 100% inactive (000 2000 sec.) 0 1.065 1.583 1800 100% inactive 5 1,050 1,526 1800 100% inactive 7.5 1.116 1.662 1823 100% inactive 10 1,111 1,638 1820 50% inactive + _ 50% active CAA 30 sec. 0 1,056 1,563 1830 50% inactive + _ 50% active CAA 30 sec 2.5 1.038 1.519 1835 50% inactive + 50% active 000 30 sec. 5 1,038 1,095 1800 50% inactive + 50% active 000 30 sec. '0 1,052 1,552 1836 50% inactive + 50% active 000 30 sec. "2.5 1.038 1.515 1837 50% inactive + 50% active 000 30 sec. 5 1,002 1,506-1802 50% active CAA 30 sec. + 50% akviv 000 30 sec. 2.5 1.060 1.559 1837 CAA = citric acid activity. 450 496 *Sample (Ring 1) (Ring 2) (Ring 3) 20 Table II Occupancy conditions Concentration 5 / cc 0.195 0.2U8 0.225 Coating weight 5 / m _ 11.31: _ 15.12 11,311 450 496 =@w.Q w fi æ fl @mm. fi mmw.Q Ozæ fl> ~ m.H Apmwc fi p m> m Hm » n fi wumëv flfl o fi ucom 1 .. 2 ^ nwwG fi n m nww.ø ønw fi ¶> ~ m. fi >>>. 0 O = w fl @ fi m.H> @ Hwv fl wøwsv cw nwcwc fl wwaas uww fi : cm Sowv fi moaäom. _ ~ ¿«¶> onm s \ <mm »ø fl>» mom Nmow: Oo H uwa fififi pwwe: Oo aßa fi a \ <wa »ø fl> @«> wx \ @ »@ = »Pmm> fi p @ ~ wm u fl> wx \ p» «: pwp flfifi nmwsnma> fi» @ H «m wucwp flfi m wucmpwm mm mxmcm 0 mxmwuwc mä HHH H fl wnmß _ .... .......-__...-__.... ...

Claims (14)

450 496 22 Patent claims A composition for forming a non-conductive glass film on surfaces P of oriented silicon alloy steel and sheet metal thereof. comprising a slurry 1 water of magnesia and a phosphate-containing precursor! selected from the group consisting of calcium phosphates. water-soluble ammonium polyphosphate. aluminum phosphate. magnesium phosphates, phosphoric acid and mixtures thereof. where the compound is present in the range of 2% to 25% by weight. calculated as P205. based on the magnesia weight and raised substantially water. It is known that at least 25% by weight of magnesia has a citric acid activity greater than 200 seconds. that the magnesium concentration is up to 0.6 g per cm3 of slurry. and that the slurry is stable to sedimentation for periods of up to 10 hours. 2. A composition according to claim 1, characterized in that the magnesia comprises about 50% by weight of magnesia with a citric acid activity of 1500 to 3000 seconds and about 50% by weight of a magnesia with a citric acid activity of 20 to 40 seconds. Composition according to Claim 1, characterized in that the phosphate-containing compound is present in the range from 2.5 to 10% by weight, calculated as P 0. based on the weight of the magnets. Composition according to Claim 1, characterized in that the magnesia comprises 25 to 75% by weight of magnesia with a citric acid activity of 1500 to 3000 seconds and the remainder a magnesia with a citric acid activity of 20 to 40 seconds and in that the phosphate-containing compound is in the range 2.5 to 10 weight percent calculated as P205. based on the weight of the magnet. 450 493 23 Composition according to claim 1, characterized in that the magnesia comprises about 50% by weight of magnesia with a citric acid activity of 1500 to 3000 seconds and about 50% by weight of magnesia with a citric acid activity of about 30 seconds and in that the phosphate-containing compound is present in the range 2.5 to 10 weight percent calculated as P 0. Based on the weight of the magnesia. Composition according to Claim 1, characterized in that the phosphate-containing compound consists of monocalcium phosphate monohydrate. dicalcium phosphate dihydrate or water-soluble ammonium polyphosphate. Composition according to Claim 2, characterized in that. . H 3. the magnesium concentration is at least 0.24 g / slurry. Composition according to claim 4, wherein the silicon alloy steel has a very high permeability, characterized in that the phosphate-containing compound is in the range 5 to 10% by weight calculated as P 2 O 5. and comprising 0.10 t to 0 '0 0.15% boron and 5% to 10% titanium dioxide. based on the weight of the magnesia. 9. A method of suspending an inert magnesia in water to produce a slurry which is stable against sedimentation and which, after being applied to the surfaces of oriented silicon alloy steel strip or sheet metal, will react with the silicon in the steel to form a slurry. insulating glass film during a subsequent annealing at high temperature. which method comprises preparing a slurry containing magnesia and a phosphate-containing compound in the range of 2% to 25% by weight. calculated as PZOS. based on the weight of magnesia. where the compound is selected from the group consisting of calcium phosphates. water-soluble ammonium polyphosphate. aluminum phosphate. magnesium phosphates. phosphoric acid and mixtures thereof. It is known that at least 25% by weight of magnesia has a citric acid activity greater than 200 seconds. 4 450 496 24 10. A method according to claim 9, characterized in that the magnesia comprises 25 to 75% by weight of a magnesia with citric acid activity of 1500 to 3000 seconds and the remainder a magnesia with a citric acid activity of 20 to 40 seconds. ll. A method according to claim 9 or 10. characterized in that the magnesia comprises about 50% by weight of a magnesia with a citric acid activity of 1500 to 3000 seconds and about 50% by weight of a magnesia with a citric acid activity of 20 to 40 seconds. A method according to any one of claims 9 - 11. characterized in that the phosphate-containing compound consists of monocalcium phosphate monohydrate or dicalcium phosphate dihydrate and is present in the range 2.5 to 10% by weight calculated as P 2 O 5. based on the weight of magnesia. 13. A method according to any one of claims 9 - 12, characterized in that from 0.120 to 0 is added to the slurry. A method according to claim 11. know that the magnesium concentration in the slurry is at least 0.24 g l 0.. 3. and extends up to 0.6 g / cm slurry.